including/require_once problem in my php file.

Hi. I have created a custom button in subpanel of my module. Actually I want when I click this custom button it opens a popup window where all the data from my database is shown. This custom button is linked to a popup window file called pop.php that I created myself, it is located in sugar/custom/pop.php. When I include files in pop.php, it does not work, in short no php file is included in this pop.php file. Please help me how can I connect to database from this file ? Why any file is not including in pop.php. I have used require_once, include_once, include etc. but no one is working in pop.php.I am using SugarCRM 6.5 CE